Have you come across any particularly striking initial puzzle square arrangements? There are many interesting star and loop patterns that you sometimes see in magazines and newspaper. I wonder if a 'pretty' pattern makes it a harder or an easier puzzle to solve.

No I don't rate the prettiness of the puzzle that highly. Much more important to have an interesting puzzle to solve. I haven't noted any correlation between 'prettiness' and 'difficulty'. In any case the initial pretty layout is soon lost when you start solving squares.